1. Field of the Invention
The invention generally relates to systems and methods for the environmental remediation of materials contaminated with heavy minerals. More particularly, the invention relates to systems and methods for removing heavy minerals from materials such as soil, mine tailings, sediments and ores without the use of water or the creation of dust.
2. Description of the Related Art
Some heavy minerals can pose an environmental threat due to their toxicity to living systems. Unlike organic pollutants, toxic heavy minerals once introduced into the environment cannot be biodegraded. They persist indefinitely and cause pollution of air, water, and soils. Thus, the main strategies of pollution control are to reduce the bioavailability, mobility, and toxicity of the minerals. Methods for remediation of toxic heavy mineral-contaminated environments include physical removal, detoxification, bioleaching, and phytoremediation. Lead, mercury, cadmium lithium, manganese, thallium, tin, nickel, chromium, aluminum, and zinc are but a few examples of heavy minerals that can have toxic effects in their elemental form, or through the formation of toxic compounds. Metal toxicity or metal poisoning is the toxic effect that certain metals have on living organisms. In the case of lead, any measurable amount may have negative health effects.
Industrial manufacturing, smelting, mining activities, sedimentation and runoff are common sources of heavy mineral contamination. The predominance of these sources of contamination create a widespread need for devices and methods that are capable or addressing these environmental problems. Heavy mineral contamination poses risks for both municipal and wildlife concerns. For example, heavy minerals pose a risk to aquatic wildlife as well as municipal sources of drinking water such as reservoirs and ground water.
The toxic effects of heavy minerals in aquatic environments (e.g. streams, creeks, lakes and rivers) is surprisingly similar to that outside a water body. Sediments in aquatic environments exhibit the same binding characteristics found in the normal soil environment. As a result, many heavy minerals tend to be sequestered at the bottom of water bodies. Some of these minerals will dissolve. The aquatic environment is more susceptible to the harmful effects of heavy mineral pollution because aquatic organisms are in close and prolonged contact with the soluble minerals.
Soils may become contaminated by the accumulation of heavy metals and metalloids through emissions from rapidly expanding industrial areas, mine tailings, disposal of high metal wastes, leaded gasoline and paints, land application of fertilizers, animal manures, sewage sludge, pesticides, wastewater irrigation, coal combustion residues, spillage of petrochemicals, and atmospheric deposition. Toxic heavy metals constitute an ill-defined group of inorganic chemical hazards, and those most commonly found at contaminated sites are lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni). Soils are the major sink for heavy metals released into the environment by the aforementioned anthropogenic activities, and unlike organic contaminants which are oxidized to carbon (IV) oxide by microbial action, most metals do not undergo microbial or chemical degradation and their total concentration in soils persists for a long time after their introduction. Changes in their chemical forms (speciation) and bioavailability are, however, possible. The presence of toxic heavy metals in soil can severely inhibit the biodegradation of organic contaminants. Heavy metal contamination of soil may pose risks and hazards to humans and the ecosystem through: direct ingestion or contact with contaminated soil; the food chain (soil-plant-human or soil-plant-animal-human); drinking of contaminated ground water; reduction in food quality (safety and marketability) via phytotoxicity; reduction in land usability for agricultural production causing food insecurity; and land tenure problems.
There are several methods for the remediation of environmental contamination due to toxic heavy minerals. These methods include excavation of soils wherein a contaminated material, such as soil, is collected and taken to a disposal site. This method of remediation however potentially requires the transport of large volumes of material only a small portion of which comprises the heavy mineral. Thus, large volumes of material are extracted in an effort to remove a small amount of heavy mineral. In addition, the material removed must oftentimes be replaced. Aeration is another method of removing heavy minerals (e.g. heavy metals) from a contaminated area, but this method creates air pollution and further disperses the contaminated heavy minerals.
Leaching and sluice boxes also provide a means for removing heavy minerals from contaminated materials. These methods however require the use of large volumes of water which may not be available near sites where environmental remediation is desired. In fact, locations where environmental remediation of heavy minerals is desired is often remote and far removed from any practical source of water. Moreover, even in locations where a source of water is available, the scarcity of water and the competing needs of municipal, agricultural and wildlife uses makes the use of water for environmental remediation impractical.
What is needed in the art therefore are water-free, dust-free systems and methods for the removal of heavy minerals from contaminated materials such as soils, sediments and ores.